The invention relates to an apparatus for recording sound on an audio-information recording medium, preferably utilized in a motion-picture camera, the recording apparatus including a recording head to which are applied both audio-frequency audio signals and also higher-frequency magnetic biasing signals.
With such sound-recording apparatuses, it is necessary that the audio-frequency audio signal to be recorded be applied to the sound recording head in super-position with a constant magnetic biasing current whose amplitude is independent of changes in the frequency of the audio signals.
The impedance of the induction coil of the recording head and likewise the current flowing through the induction coil is frequency-dependent. Accordingly, it has been proposed to connect a biasing resistor in series with the induction coil, the resistance of the biasing resistor being large compared to the induction-coil impedance at the highest frequency of the signals applied to the induction coil. The greater the resistance of the biasing resistor, the closer is the approximation to a frequency-independent audio-frequency constant-current source. However, this expedient has the disadvantage that the large resistance of the biasing resistor reduces the sensitivity and therefore the efficiency of the recording means.